4. Server Architecture

Digital Rebar Provision is provided by a single binary that contains tools and images needed to operate. These are expanded on startup and made available by the file server services.

4.1. Services

Provisioning requires handoffs between multiple services as described in the Workflows section. Since several of services are standard protocols (DHCP, TFTP, HTTP, HTTPS), it may be difficult to change ports without breaking workflow.

The figure below illustrates the four core Digital Rebar Provision services including protocols and default ports. The services are:

  1. API - These services provide control for the other services
    1. Service API: REST endpoints with Swagger definition
    2. UI: User interface redirect and local UX
    3. Webscoket interface
    4. Swagger UI interface
  2. DHCP: Address management includes numerous additional option fields used to tell systems how to interact with other data center services such as provisioning, DNS, NTP and routing.
  3. Provision: sends files on request during provisioning process based on a template system:
    1. TFTP: very simple (but slow) protocol that’s used by firmware boot processes because it is very low overhead.
    2. HTTP: faster file transfer protocol used by more advanced boot processes
    3. HTTPS: faster file transfer protocol used by more advanced boot processes
  4. RAFT: Synchronization and High Availability Support
    1. RAFT: Consensus protocol for maintaining state with the high availability cluster.
Core Digital Rebar Provision Services

4.2. Ports

The table describes the ports that need to be available to run Digital Rebar Provision (DRP). Firewall rules may need to be altered to enable these services. The feature column indicates when the port is required. For example, the DHCP server can be turned off and that port is no longer required.

Ports Feature Usage
67/udp DHCP DHCP Port
69/udp PROV TFTP Port
4011/udp BINL PXE/BINL port
8080/tcp Metrics Prometheus Metrics
8090/tcp PROV HTTPS-base Dynamic File Server
8091/tcp PROV HTTP-base Static File Server
8092/tcp Always HTTPS API and Swagger-UI
8093/tcp RAFT High Availability Protocol

All default ports can be changed at start up time of the dr-provision service. NOTE that changing DHCP and TFTP ports has wide ranging implications and is likely not a good idea (many firmware implementations can not be changed to use alternate port numbers).

Port access requirements:

In all provisioning usage cases (67, 69, 4011, 8090, 8091, and 8092) the ports from the Machines being provisioned to the DRP Endpoint must be accessible. The DRP Endpont must be able to reach the Machines being provisioned on port 67. In addition, the API and Swagger-UI port must be accessible to any operator/administrator workstations or systems that are controlling and managing the DRP Endpoint service. Additionally, any services or integrations that interact with the DRP Endpoint (eg IPAM, DCIM, Asset Management, CMS, CMDB, etc) may need access to the API port. BINL is an optional protocol and only needed if you are using it in place of PXE.

If you are running drpcli info status or drpcli info check from another host, make sure firewall rules are in place to allow communication between both the host and the endpoint as both commands check all ports on the DRP endpoint.

Optionally, the DRP Endpoint MAY use the HTTPS (443/tcp) or SSH port (22/tcp) to connect to machine remotely. This is an OUTBOUND port usage. It is a common usage for Terraform and Ansible execution from the DRP Endpoint.

Within an HA cluster, the DRP Endpoints MUST be able to bi-directionally communicate over the RAFT port. HA is an optional configuration.

Additionally, the DRP Endpoint can export Prometheus metrics, and by default metric service will run on port 8080. If you wish to scrape DRP metrics, you will need to accommodate this port as well.

Here is an example of Linux based IPTables firewall rules. Note that you may need or be required to restrict the source IP addresses appropriately for your operational security requirements. For example, the Machines that will be provisioned need access to all ports, and administrators/operators may need access to the API port for control plane of the DRP Endpoint(s). You will need to adjust the input interface (-i eno3) appropriately for your system.

# a vague attempt to make this roughly reusable...
INTERFACE=eth0
PORT_DHCP=67:68
PORT_TFTP=69
PORT_SFILE=8090
PORT_FILE=8091
PORT_BINL=4011
PORT_PROV=8092
PORT_PROM=8080
PORT_RAFT=8093
SOURCES=""       # add appropriate "-s IP/netmask" etc statements here

# for local connectivity
iptables -A INPUT -i lo -p tcp -m tcp --dport $PORT_FILE -j ACCEPT
iptables -A INPUT -i lo -p tcp -m tcp --dport $PORT_SFILE -j ACCEPT
iptables -A INPUT -i lo -p tcp -m tcp --dport $PORT_PROV -j ACCEPT

# adjust input interface appropriately
iptables -A INPUT -i $INTERFACE $SOURCES -p tcp -m tcp --dport $PORT_FILE -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p tcp -m tcp --dport $PORT_SFILE -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p tcp -m tcp --dport $PORT_PROV -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p udp --dport $PORT_BINL -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p udp -m udp --sport $PORT_DHCP --dport $PORT_DHCP -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p udp --dport $PORT_TFTP -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p tcp -m tcp --sport $PORT_RAFT -j ACCEPT
iptables -A INPUT -i $INTERFACE $SOURCES -p tcp -m tcp --dport $PORT_RAFT -j ACCEPT

If your DRP Endpoint is listening on multiple network interfaces, you will need to adjust these rules appropriately.